The Use of Peel Tests to Examine the Interfacial Strength of SEBS Modified Interfaces between Immiscible Homopolymers

Abstract

The relative interfacial strengths of poly(styrene-block-ethylene/butylene-block-styrene) triblock copolymers (SEBS) modified interfaces of immiscible polymers, polystyrene (PS) and low density polystyrene (LDPE), has been studied using peel test. Specimens were prepared by spin coating thin SEBS triblock copolymer films from solution onto LDPE slabs. After spin coating and drying in a vacuum oven at 40oC for several days, the LDPE slabs were placed on top of PS slaps, forming the “sandwich” arrangement. The 90o peel test arrangement was employed because the PS is stiff at room temperature whereas the LDPE is flexible. For thin copolymer layer (expected to leave the interface unsaturated), the trend in variation of interfacial strength with copolymer molecular weight was observed. However, for thick layers (oversaturating interface) the interfacial strength became in one case too large to separate the layers in the peel test. This may suggest a different mechanism for increasing interfacial strength when at least one of the copolymer blocks is crystallisable. Moreover, the microstructure morphology of the copolymers at the interface is expected to change during annealing time since it was found that the interfacial strength changed with annealing time.